Synthetic paper has proposed and put into practical use in recent years in place of conventional natural pulp-made paper, where the synthetic paper comprises a base layer made of a biaxially stretched polypropylene film containing 5 to 40 wt % of an inorganic fine powder, and a paper-like layer stacked on the top and back planes thereof, which is made of a uniaxially stretched polypropylene film containing 8 to 65 wt % of an inorganic fine powder (U.S. Pat. No. 6,418,950, Japanese Examined Patent Publication Nos. 46-40794, 60-36173 and 62-35412).
Offset printing, so-called lithograph, is generally applied for printing on paper, polyethylene terephthalate film, polyamide film, coated paper and the like, since the technique can readily provide multi-color printing. Typical composition of a general-purpose, dry-type offset printing ink is shown below.

TABLE 1Composition of Offset Printing Ink (weight part)ink forink forink forsheetnon-paperrotary offsetprintingprintingpresspigment252525resin253025drying oil203410high-boiling-point,25 536petroleum-base solventdrier 1 2—others 4 4 4total100100100
The vehicle described in the above refers to a liquid component among various components composing printing ink, and is responsible for dispersing pigment to thereby keep fluidity of the ink; for ensuring smooth movement of the ink from an ink pot to a printing plane after being transferred among individual rollers, plate and blanket; and for fixing the pigment onto the printing plane through solidification. In response to recent strong requirement to shorten the drying time of the offset printing ink for more rapid printing, there is an increasing trend of using quick-drying ink having compounded therein a vehicle which mainly comprises a drying oil added with resin and mineral oil (high-boiling-point, petroleum-base solvent).
Printing with such quick-drying offset printing ink on the synthetic paper comprising a polyolefinic film or such film compounded with an inorganic fine powder, however, undesirably swells the polyolefin per se due to the vehicle contained in the quick-drying offset printing ink to thereby produce local surface waving or curling of the printed film, which has been an obstacle for the practical use. So that the conventional offset printing ink for polyolefinic film has been such that having a special formula without mineral oil at the sacrifice of the quick-drying property.
Such special offset printing ink for polyolefinic film, however, requires long drying time and has been only available in limited printing works and manufacturers, so that there has been a strong need for a new polyolefinic film on which the general-purpose offset printing ink of oxidation polymerization type (drying oil type) is available.
That is, in the general printing works, offset printing is practiced on pulp-base paper such as wood free paper and coated paper using generally-commercialized, quick-drying ink, so that printing on the polyolefinic film or synthetic paper requires temporary replacement of such ink with the special offset printing ink suitable for such non-absorbent material. Such replacement of the ink is, however, considerably time- and labor-consuming, so that the general printing works have not been positive about printing on the polyolefinic film or synthetic paper, which has been one factor obstructing the generalization of the polyolefinic film or synthetic paper in offset printing.
One approach has been made (Laid-Open Japanese Patent Publication No. 8-333466), in which a polyolefinic resin added with an amorphous resin is used as a part of the multi-layered film. Such technique is, however, still not successful in solving the problem of swelling of the film (referred to as “solvent attack” hereinafter) as a whole due to vehicle (in particular high-boiling-point, petroleum-base solvent such as mineral oil) contained in the offset printing ink.
It is therefore an object of the present invention to provide a multi-layered stretched resin film excellent in ink drying property, and less causative of surface waving or entire curling even if the film is subjected to offset printing using a general-purpose, quick-drying offset printing ink.